1. Field of the Invention
The present invention relates to a backlight device using a light-emitting diode element, and to a liquid crystal display device.
2. Description of the Related Art
In recent years, a thin and lightweight module structure is indispensable for a liquid crystal display device. The performance is required to be maintained or improved while, with regard to members mounted on the module, the number of the members is sought to be reduced and thinning and reducing weight of the members are sought. With regard to a backlight source module of a large liquid crystal display device, it is made possible to, using a light-emitting diode element, widen the range of color reproduction, improve high-speed independent control which accommodates moving images, and improve contrasts compared with a conventional cold-cathode tube. However, it is still necessary to take measures for a thinner and lighter size. With regard to heat radiation, it is also important to maintain the thin and light size while a heat radiation structure is formed.
When a light-emitting diode element is used to form a thin and lightweight backlight source module, it is necessary that members mounted thereon and a connection structure are simplified to accommodate a thin and light size. The following documents disclose packages of backlight source modules which reduce the number of members mounted thereon and which are adapted for simplified connection.
JP 2001-345485 A discloses a structure in which a pair of metal layers are provided on a front surface and a rear surface of a package base material to materialize a more compact package, and heat is radiated by connecting the metal layers via a metal connecting portion. This makes, when a plurality of light-emitting elements are mounted, heat radiation properties uniform, and thus, temporal change of the color balance is reduced. JP 2006-210880 A discloses that an optical layer is laminated on a base substrate having through holes formed thereinto form a two-dimensional surface light source. This makes the light source smaller in size and simplifies a fabricating process of a backlight. JP 10-226107 A discloses that, in an optical print head having a common electrode and a light-emitting element module, a through hole for radiating heat is provided so as to pierce a substrate from a top surface to a bottom surface thereof, and a heat conductive material layer is formed on an inner wall of the through hole. This makes heat radiated via the through hole to the downside of the substrate. JP 2007-109945 A discloses that a non-flow type adhesive or a thermocompression bonding type adhesive such as a bonding sheet is applied to a mounting substrate on which arrays of a plurality of light-emitting elements are arranged in lines. This makes it possible to enhance heat radiation with no increase in cost and to effectively use light diffused by the light-emitting elements.